Revert "Document ActionController::TestCase::Behavior::ClassMethods.process"

This reverts commit 2aef9fddf8b4487a05638ea3341dfd65ceb229ef.

Reason: The added change isn't clear in terms of explaining the
arguments. Will ask the author to provide a PR and take it forward.

[ci skip]
Revert "Running AR tests on postgres, mysql & sqlite"

This reverts commit 28bd442034e0974d0a4d664076dafb8e9555816d.

Reason: Existing text was clearer imo.

[ci skip]